Electronic memory device having two portions that can be decoupled

ABSTRACT

A non-volatile electronic memory device is integrated on a semiconductor and is of the Flash EEPROM type with a NAND architecture including at least one memory matrix divided into physical sectors, intended as smallest erasable units, and organized in rows or word lines and columns or bit lines of memory cells. At least one row or word line of a given physical sector is electrically connected to at least one row or word line of an adjacent physical sector to form a single logic sector being erasable, with the source terminals of the corresponding cells of the pair of connected rows referring to a same selection line of a source line.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 14/453,360 filed Aug. 6, 2014, which is a continuation of U.S.patent application Ser. No. 11/279,385 filed Apr. 11, 2016 and issued asU.S. Pat. No. 8,824,205 on Sep. 2, 2014 which application claimspriority to Italian Application No. MI2005A000609 filed Apr. 11, 2005,Italian Application No. MI2005A000610 filed Apr. 11, 2005, EPOApplication No. 05425209.3 filed Apr. 11, 2005, and EPO Application No.05425207.7 filed Apr. 11, 2005. The aforementioned applications, andissued patent, are incorporated herein by reference, in their entirety.

FIELD OF THE INVENTION

The present invention relates to a Flash EEPROM electronic memory devicemonolithically integrated on a semiconductor and having a NANDarchitecture comprising at least one memory matrix organized in memorycell rows and columns. The invention also relates to a method forprogramming the above memory device with the NAND structure.

BACKGROUND OF THE INVENTION

It is known that the market for non-volatile memories, for example ofthe EEPROM or Flash EEPROM type, is currently growing significantly andthe most promising applications relate to the “data storage” field.Until a few years ago, such a market almost exclusively involved theconsumer field of digital cameras, with the associated memory cards, orthe known USE keys which represented expansion mobile memories forpersonal computers. Therefore, the demand for these products by theconsumer market was mainly addressed to flash memories of largecapacity.

This trend seems destined to be reinforced in the next years by virtueof newer applications of portable electronic devices which require ahigher and higher memory capacity, for example, for digital cameras ormobile phones of the latest generation operating, for example, accordingto the 3G or UMTS standard.

These applications are completely compatible with the natural evolutionof Flash memories if one considers that such memories are substantiallysolid-state mass memory units with further advantages linked to theirlow power consumption, to their operation silence, and to their reducedspace, etc.

As is well known to the skilled person in the art, the Flash memoryarchitectures are substantially referred to two fundamental paths, thefirst of which refers to the traditional and widely tested NORarchitectures, whereas the second one refers to the more innovative andpromising NAND architectures. For the previously cited applications, theflash architecture being most suitable to the requirements of lowconsumption, high density, high program and/or erase speed, is certainlythat of the NAND type. This kind of architecture exhibits advantageswith respect to NOR architectures. In particular, Flash memories withthe NAND architecture are faster in data storage activities and inmanaging large amounts of data to be restored in a synchronous way, andthis makes them more suitable to use for applications on portableelectronic devices.

Since, in data storage applications, the random access time is lessimportant than with “code storage” applications, the most significantfeature of the architectures of the NOR type loses most of itsimportance to the advantage of the NAND architecture which allowstreating large amounts of “synchronous” data in reading and programmingin a simple and quick way. However, although having the feature of asuperior data modify speed, such NAND memories do not allow fast randomaccess, since they are oriented to readings of entire pages of at least512 bytes, but not of single bytes. In fact, the NAND access protocol isquite slow in random access due to the known latency time, and itexhibits serious difficulties for acceding into a sector or a page in arandom way.

For meeting the increasing needs of portable electronic devices it wouldbe necessary to have in a same memory also an excellent random accesstime, such as to perform the code or the boot of the operating system orof the programs without the burdensome assistance of a RAM. Recently,further new needs have arisen linked to the game and cellular phonemarkets, which need the availability of high capacity memories, to storeany kind of data, but also to store an operating system, video,programs, results, etc.

To meet these needs, a technique has recently been proposed includingdevices defined as MCP (Multi Chip Package) which incorporate, in asingle package, different integrated electronic circuits such as forexample several types of memory circuits, for example one Flash memoryof the NAND type, one of the NOR type, and one RAM memory.

All these memories are assembled and supplied in a single package so asto provide a single device simultaneously having the advantages of allthe memories on the market, for example density and storage capabilitywith regard to the NAND portion, or access speed and XIP possibilitywith regard to the NOR portion, and random access with regard to the RAMportion.

One of these devices is commercially known with the acronym OneNAND andmanufactured by Samsung. Another example of this kind of Multi ChipPackage is the “DiskOnChip” of M-System.

Although advantageous under several aspects, these devices are notexempt from drawbacks. First of all, it is to be considered that thevarious memory circuits to be assembled in a single package are realizedwith different technologies that oblige addressing problems ofcompatibility in the supplies on a single package, and, in themanagement of the input/output signals.

Secondly, the costs of the resulting package cannot differ significantlyfrom the global cost of the various components, since they cannotexploit large scale economies in the realization of devices assembledwith components being different from one another.

There exist, then, a series of problems to be faced starting from theassumption that only a detailed comprehension of the phenomena apt tothe memorization of the data inside the memory cells can allowunderstanding of the intrinsic limits of the adopted technology.

For example, in the attached FIG. 1, the structure is shown of anon-volatile memory device 1 integrated on a semiconductor andcomprising a NAND memory matrix 2 of the traditional non-volatile typemade of a plurality of blocks or physical sectors organized in cell rowsand columns. This type of architecture provides a very organizedstructure of memory cells divided in two sub-matrixes 3 and 4, left Land right R, making reference to a single row decoding block 5 centrallyarranged in the device 1. A bank of registers of the read amplifiers orsense amplifiers 6 and 7 corresponds to each sub-matrix L, R.

In FIG. 1A, by way of illustration only, the matrix 2 is shown withblocks i and j of only four rows, which, however, are practically madeof at least 16 rows and four columns. Each row or word line ROW <0:3> ofa given n-th block of the matrix corresponds to a respective row driver.

It can be also appreciated that the cells of a given block or sector i,j . . . have a common source line and that they are connected to arespective bit line and to the common source line by way of respectivedrain (DSL) and source (SSL) selectors.

In summary, in the architectures of the traditional type the word linesof a matrix, both of the NOR type and of the NAND type, are independentfrom each other and the potential for selecting the cell to be read orprogrammed is applied to only one matrix row. This approach necessarilyimplies dedicated decoding networks for each sector with an increase inthe number of lines and of transistors.

This field suffers from the length of the memory cell arrays whichrequire high propagation times in the reading step for allowing reachingthe cells being farthest from the node to which the reading potential isapplied. Moreover, it is also to be noted that the lithographic sizesfor the manufacturing of non-volatile memories have reached limits lowerthan about 65 nm, or even than 32 nm, such as to make not only theconstruction of the interface between the decoding circuitry and thematrix of the cells themselves difficult, but also such as to enormouslyincrease the propagation times of the signals due to the lines length.

In this respect, an important role is played by the row decoding, whosearchitecture largely conditions both the sizes, and the access time ofthe memory. Where the row lines reach the extreme compactness levels,mainly in Flash of the NAND type, the problem becomes extreme and theimplementation complex to such an extent as to make the area occupationinefficient.

The program and erase operations occur by exploiting the Fowler-Nordheimphenomenon, while the reading is an operation of the dynamic type. Dueto this, the reading step is slowed down a lot.

It is to be remembered that in a sector of the NAND type the smallesterase unit is made of a group of word lines equal to the number of cellsof the stack included between the SSL and DSL lines which interceptthem, i.e. 16 or 32, according to the memory sizes.

This implies that each stack elemental structure has a very reducedconductivity, and thus a great limitation to the reading speed. Theconventional stack structure (16, 32 cells) is thus intimately slowsince it is not very conductive.

Finally, it is to be signaled that current NAND memories do not allowperforming an operating code, for example of the XIP type, since therandom access time typical of these architectures is on the order of10-20 μsec. The reason for such slowness is due to the particularorganization of the matrix which normally comprises groups of 16/32cells in series, which strongly reduces its conductivity, connected toeach other through long selector lines, which significantly decreasestheir propagations with long bit-lines that strongly burden the load.

The increase of the load due to the BL is significantly greater than inthe corresponding NOR-Flash since, in the NAND-Flash, the generic BLcollects the capacitances of all the stack or column structures which,combined with the large capacitances of the memory, remarkably increaseits value.

SUMMARY OF THE INVENTION

The present invention is directed to providing a matrix architecture fora non-volatile electronic memory device of the monolithically integratedtype, i.e. realized on a single chip, having such structural andfunctional features as to incorporate a memory matrix divided into atleast one pair of portions having different data storage capacities anddifferent access speed.

A further object is that of providing a memory device of the indicatedtype and having structural and functional features of greatercompactness, so as to simplify the modes of access to the memory,overcoming the limits and the drawbacks of the known technique.

Another object of the present invention is that of providing a type ofelectronic memory device having such structural and functional featuresas to offer the same performances as a Multi-Chip Package, however,overcoming the limits and the drawbacks of that type of approach.

A further object of the present invention is that of providing a type ofelectronic memory device wherein the two portions of memory matrixhaving different data storage capacities and different access speeds canexploit the same structural sources but can be decoupled according tothe operation needs of the user.

Still a further object of the invention is that of providing theintroduction, with respect to the traditional methods, of a selection ofthe matrix rows so as to minimize the cell network and make more simplethe realization thereof.

The present invention realizes a memory integrated architecture havingat least two areas or portions with different data storage capacitiesand different access speeds, which exhibit continuity between the bitlines structures and share both the read and program resources, whichmaintain the same protocol and operating management procedures, andwhich tolerate different propagation and conductivity times in the twosections.

More particularly, the memory integrated architecture has a fastestsection that includes measures suitable to improve its conductivity, toreduce the propagations, to minimize the load.

The same fastest section implies physical sectors melded with each otherby multiples of two, four, etc., short-circuiting the pairs of wordlines with each other, for example short-circuiting a row of a physicalsector with a corresponding row of the adjacent physical sector, thusobtaining a logic sector which becomes the smallest unit entirelyerasable by the new architecture. In any case the integrity of the datais maintained in each array cell safeguarding, in the meantime, thefunctionality of the structure, the correspondence between the rowsbeing moreover definable according to the needs of the device layout.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the electronic memory device and of therelative programming method according to the invention will be apparentfrom the following description of an embodiment thereof given by way ofindicative and non-limiting example with reference to the annexeddrawings.

FIG. 1 shows a schematic view of electronic memory device, in particularan EEPROM memory with NAND architecture, realized according to the priorart.

Figure IA shows a schematic view of a portion of electronic memorydevice, in particular an EEPROM memory with NAND architecture, realizedaccording to the prior art.

FIG. 2 shows a schematic view of an electronic device memory, inparticular an EEPROM memory with NAND architecture, realized accordingto the present invention.

FIG. 3 shows a schematic view of the electronic memory device accordingto the present invention, where a measure is highlighted for decouplingthe bit lines shared by two portions of the cell matrix.

FIG. 4 shows a further schematic view of the device of FIG. 3.

FIG. 5 shows a schematic block view and in greater detail, of a portionof the device of FIG. 3.

FIG. 6 shows a schematic view of a portion of the electronic memorydevice, in particular, an EEPROM memory with NAND architecture, realizedaccording to the present invention.

FIG. 7 shows a further way to illustrate the same memory portion,according to the present invention, already shown in FIG. 6, andhighlighting the biasing values of bit lines in the programming step.

FIG. 8 shows a schematic view of a portion of electronic memory devicerealized according to the best realization mode of the present inventionby way of a different coupling of word lines with respect to the exampleof FIG. 7.

FIG. 9 shows a comparative table reporting the biasing values of the rowand column selectors of the well region wherein the memory cells arerealized for a matrix portion according to the prior art and for thematrix portion according to the invention, respectively.

FIG. 10 shows a schematic view of the portion of FIG. 7 during thereading step of a memory cell.

FIG. 11 shows a schematic view of the portion of FIG. 7 during theerasing step of a sector of the memory matrix.

FIG. 12 shows a schematic view of the portion of FIG. 7 during theprogramming step of the content of a memory cell.

FIG. 13 shows, on a diagram with same time basis, the trend of a groupof signals of the programming step of the memory matrix portionaccording to the invention, for optimizing the functionality thereof.

FIG. 14 shows a schematic view of a portion of the memory device,according to the invention, wherein a single selector block is providedfor two word line groups.

FIG. 15 shows a schematic view of the device of FIG. 3 wherein thefluidification technique of the propagations according to the WL by wayof the metal strap on the word lines of the fast memory portion ishighlighted.

FIGS. 16, 17A, and 17B show respective schematic views of an embodimentof strap techniques for the device, according to the invention.

FIG. 18A shows a schematic view of a possible edge strap technique inaccordance with the present invention.

FIG. 18B shows a schematic view of a possible edge strap and of fullmiddle strap technique for the device of the present invention;

FIGS. 19 and 20 show respective schematic views of further embodimentsof strap techniques according to the invention.

FIG. 21 shows a schematic view of the device of FIG. 3 wherein portionsof slow, fast, and intermediate speed portions are highlighted betweentwo realized according to the present invention.

FIG. 22 shows a schematic view of the semiconductor package inherent inthe memory device of FIG. 2, wherein the main input/output pins arehighlighted.

FIG. 23 shows a more detailed schematic view of an embodiment of thefast matrix portion, in accordance with the invention.

FIG. 24 shows a schematic example of how an increase of conductivity ofthe elemental AND structures of the fast matrix portion is achieved byoperating parallelisms of word lines on the basis of two or on the basisof four, in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the Figures, and in particular to the example of FIG.2, an electronic memory device is realized and monolithically integratedon semiconductor.

The device 20 incorporates at least one matrix 21 of memory cellsorganized in rows or word lines WL and columns or bit lines BL. Thedevice 20 is, however, a memory of the Flash EEPROM type with a NANDarchitecture. FIGS. 6 and 8 show, instead, two possible implementationsof the array relative to the fast sections 23 a and 24 a of Flash EEPROMmemory with NAND architecture of the device 20.

The memory allows, to the expense of a slight modification of the arrayof a NAND memory, to realize in a single chip, and thus with a singletechnology, a group of functions being typical of different memories andup to now obtained only by way of devices of different nature andstructure. In other words, the device 20 is realized on a single chipwhich integrates both the “hard disk” and boot ROM functions, avoidingthe use of the assembly of several components coming from differenttechnologies, even if arranged on a same package.

As already previously seen, FIG. 1 shows a schematic view of electronicmemory device 1, in particular an EEPROM memory with NAND architecture,realized according to the prior art. This type of architecture providesa very organized structure of memory cells divided into two sub-matrixes3 and 4, left L and right R, referring to a single row decoding block 5centrally arranged in the device 1.

Each one of the sub-matrixes 3 and 4 corresponds to a bank of registersof the read amplifiers or sense amplifiers 6 and 7. It should be notedhow both the Wl and the Bl are continuous and global lines, without anyfragmentation.

Thanks to this particularly organized structure, the area consumed bythe array is reduced and significant memory capacities can be easilyobtained even of a 1 Gigabit or up to a 2 Gigabit and more.

With this advantage also different drawbacks are however associated. TheWl are very long and thus resistive, capacitively heavy, and definitelyslow to propagate the signal up to the array edges. The Bl are in turnvery long, they collect a very high number of nodes which, summing anenormous capacity, create a load which causes extremely long times inthe read transistors. Finally, the elemental structure of each sectorexhibits a great number of devices in AND configuration (16, 32, asreported in FIG. 26), which drastically reduces the conductivity andwhich, consequently, will not impose fast dynamics in the verify step.

A new architecture of NAND electronic memory device 20 is proposedwherein inside a same sub-matrix 23, 24, L or R, a smaller, or howeverreduced, sub-matrix portion 23 a, 24 a has been obtained, for example of32 Megabit or 64 Megabit on global 1 Gigabit. The consequence of thissubdivision is the realization of two portions whose bit lines BL haveremarkably different sizes and capacitive weights, for example: shortand light for the fast portion, and long and heavy for the slow portion.The impact of this choice on the evaluation times will not be negligibleat all.

Moreover, such portion 23 a or 24 a, advantageously placed immediatelyclose to the register and read structures is operating, thanks tosuitable measures of array (FIGS. 23, 6 and 7), of WL features (FIG. 15)and techniques for lightening of the load (FIG. 3, 4, 15) at a higherspeed than the classical NANDs, i.e., with access times being comparableto the most performing architectures of the NOR type.

Hereinafter, reference will be often made to only one of the two submatrixes L, R, for example the one indicated with 23 a, using for it theterm matrix.

As it can be appreciated from the example of FIG. 2, the matrix portion23 a hereafter called “fast” is contiguous to a major matrix portion 23called “slow”, which is the higher part thereof with further connectionfunction with the read & modify interfaces. This peculiarity allows twoimportant advantages to be achieved: it ensures size compatibility andcontinuity of the lines crossing the different matrix portions, and itallows a perfect “lightening” of the load for the fast portion with thevaluable consequence of speeding up the pre-charge & verify operations.

It is important to remark that when we speak about size compatibilityand continuity of the lines we mean that the two fast and slow sectionsexhibit the same number of Bl and that each Bl of the one is thecontinuation of the homonymous of the other, being the portion Blseparated only by a device_switch 29, i.e. a pass transistor or a simpletransistor switch.

The device_switch 29 has a fundamental function on the definition of theperformances of the two portions. In fact it permits to “capacitivelydecouple” the B1 of the fast portion (short and light) from the Bl ofthe slow portion (long and capacitively heavy) consequently facilitatingthe speed of the first portion 23 a.

Therefore, any time one operates on the fast portion, said device_switch29 is made ‘OFF’ with the aim of minimizing the load and allowing themaximum speed thereof. To the contrary, when one operates on the slowportion said device_switch is maintained ‘ON’ thus establishing thecontinuity between the Bl of the two sections, and the readings whichare started therein will have response times aligned to those of aconventional NAND_Flash. The fact that the MAIN Bit Lines can beinterrupted is important, for example between a first and a secondphysical or logical sector adjacent to the column decoding. The switch29 decouples the capacitive loads of the MAIN Bit Line BL obtaining afunctional separation of the main bit line.

A further measure which distinguishes the fast portion 23 a and improvesits performances is the adoption of “Wl strap techniques”, which, widelydescribed hereafter, allow the fundamental reduction of the propagationtimes of the selection signals.

The feasibility of the improvement is made possible by the particularmanagement of the Wl of the fast portion as reported by FIGS. 6, 8, 14together with the innovative operation modes shown in the FIGS. 10, 11,12, 13 and summarized in the table 1 of FIG. 9.

Advantageously, the portion 23 is apt to data storage and it comprisesblocks being compatible with the features of a non-volatile memory ofthe Flash type which, although slow, allows a significant reduction inthe occupation of circuit area. In other words, the portion 23 is athigh density of memory cells.

With the data storage portion 23 a corresponding row decoder 25centrally arranged in the device 20 between the two sub-matrixes 23 and24 is associated. Similarly, with the code storage portion 23 a acorresponding row decoder 25 a centrally arranged in the device 20between the two sub-matrixes 23 a and 24 a is associated.

The cells with which the portion 23 a of the fast type is constructedhave the same electrical characteristics as those of the cells of theportion 23 of the “slow” type, i.e. they are programmed and erasedaccording to identical modes, but they are organized in such a way as tooperate with a higher read current. The conductivity increase of theelemental AND structures of the fast portion is advantageously obtainedsimply by reducing the number of the devices: four instead of 16 or 32(FIGS. 6, 8, 23) but it can be also thought, in an alternative way, asoperating parallelisms on basis 2 or on basis 4 as shown in FIG. 24.

A great advantage deriving from the proposed approach lies in themanagement of the different functions (Pg, Er, Rd) of the fast portion23 a shared with the slow portion 23. This peculiarity has beendeveloped on purpose so as to avoid additions and/or modifications to atraditional NAND architecture, preserving the low current consumptionand a high write/erase speed philosophy.

Summarizing, the structure of a non-volatile electronic memory device 20is monolithically integrated on a semiconductor of the Flash EEPROM typewith a NAND architecture, comprising at least one memory matrix 21organized in rows and columns of memory cells but having the peculiaritythat the matrix is divided into at least a first portion 23 and a secondportion 23 a having different data storage capacity and different accessspeed, although sharing the same bit lines structures. The second matrixportion 23 a is faster and it has lower sizes with respect to the firstmatrix portion 23. For example, the second portion 23 a can be of 32Mbit or 64 Mbit on global 1 Gbit of the portion 23, as shown in FIG. 5.

Moreover, the second portion 23 a operates with access times comparableto the NOR memory architectures, even if the cells with which the secondportion 23 a is constructed have the same electrical characteristics asthose of the cells of the first portion 23. In other words, the memorycells with which the second portion 23 a is constructed are programmedand erased according to identical modes with respect to the cells of thefirst portion 23, but they are organized in such a way as to operatewith a higher read current.

Advantageously, the second portion 23 a comprises groups of four cellsin series with the associated selectors. Current NAND memories do notallow running an operating code, for example of the XIP type, since therandom access time typical of these architectures is on the order of the10-30 μsec.

The reason for such slowness is due to the particular organization ofthe matrix which normally comprises groups of 32 cells in series whichsignificantly reduces its conductivity, connected with each other by wayof long lines of selectors affected by significant slowness with respectto the signal propagations.

Moreover, each physical sector refers, with its own elemental aconsiderable capacitance value.

Such great capacitance, combined with the very low conductivity of theelemental structures of a conventional NAND_Flash, causes very longverify times. The idea of a single Bl, which collects the nodes of allthe intersected sectors, perfectly responds to Bl compactness andminimization criteria but it may be disastrous and limiting for thedynamic aspect which results in extremely slowness. The slowness is welltolerated for the applicative part relative to “Data Storage”activities; it is instead intolerable and it cannot be proposed where aquick response is needed, as required by applications of executablecodes: “Data_Code”.

Normally, the cell matrix is divided only into the two sub matrixes 3and 4, L and R, shown in FIG. 1. The portion 23 a, which is limited insize and lightened of most the load, is fast and suitable to performexecutable codes.

In fact, the cell matrix or sub matrix structured with the two slow 23and fast 23 a portions can be used for storing in these portions data ofdifferent type, for example, a portion 23 a can be intended for codestorage activities and the other portion 23 can be intended to datastorage activities.

The portion 23 being apt to the data storage has a size equal to 1 Gbitand it follows the traditional organization of the NAND cells withgroups of sixteen/thirty-two cells with relative selectors and it canwell tolerate a capacity of bit line of about ˜5 pF.

The portion 23 a, being apt to code storage, can be instead of suitablesize, according to the users' needs, a size from eight to 16 Mbit seemsto be enough for a program or system memory.

For example, FIG. 5 schematically shows the various logic sectors of thefast portion 23 a with each sector made of eight rows (4+4 wired) and 16k columns for a total of thirty-two sectors suitable to form an 8 Mbitmemory per code storage. Whereas in the second portion 1024 sectors of16 rows and 16 k columns are shown for a total of 1 Gbit of datastorage. However, nothing forbids providing, for the portion 23 a, asize of also 32 Mbit or 64 Mbit, obviously reducing the attainableperformance.

Moreover, the bit line of this portion 23 a, although maintaining thedirect connection with the underlying part, is advantageously decoupledfrom the corresponding bit line of the portion 23 apt to the datastorage (for this reason it is placed as terminal section) by way ofpass transistors which will be hereafter called data bank selectors, butwhich do not expressively refer to the present invention.

The decoupling is activated any time a cell of the portion 23 a is read(but it can also interest the modify operations). The decoupling isactuated by placing the pass transistors 29 in the “OFF” state, forexample by forcing a GND potential onto the bank selector line.

Where, instead, it should be operated on the slow part (first portion23), the decoupling is prevented by maintaining the pass_transistors inthe “ON” state, for example by forcing a logic value ‘1’ always onto thebank selector line. In this context the portion 23 a acts as acommunication bridge between the portion 23 and the read-modifyregisters. Therefore configurations of 131 and verifications on the sameoccur by way of the portion 23 a.

More particularly, as clearly shown in FIG. 4, the bit lines of the twomemory matrix portions 23 and 23 a, slow and fast, substantially havethe same structure and they can be considered common to the two portions23 and 23 a. However, the presence of a pass transistor 29 inserted ontothe bit line in correspondence to the separation between the two matrixportions 23 and 23 a allows decoupling a long capacitance of bit lines,and, to obtain at least a matrix portion 23 a with a bit line of lowerextension. As per construction, therefore, the Bl is much lesscapacitive and therefore it can be, as any other parameter, more easilymanaged and realize faster dynamics.

The decoupling operation, absent in the conventional memories, may notbe necessary for maintaining the functionality of the portion 23 a topropagate the signal downstream of the same.

Advantageously, the various pass transistors 29, each inserted onto acorresponding bit line between the slow matrix portion 23 and the fastmatrix portion 23 a, are connected in parallel with each other and theyrefer to an enable block 28 centrally arranged in the device 20 betweenthe two row decoders 25 and 25 a.

In summary, the device 21 is characterized in that the bit line of thesecond portion 23 a is decoupled with respect to the corresponding bitline of the first portion 23 by way of pass transistors or bankselectors.

On the other hand, by decoupling the bit lines, the capacitance of thebit line of the portion 23 a, in the here described embodiment by way ofindicative example of 32 and 64 Mbit, is reduced to a value equal to1/32 and 1/16 with respect to the totality corresponding to the twoportions 23 and 23 a.

Preferably, such portion 23 a comprises groups of four cells in serieswith the relative selectors. The groups are organized with wired wordlines, as will be shown hereafter in the description with reference tothe Figures from 6 to 13.

The reduction of the number of the transistors in series allows asignificant increase of the working current. With this measure, andreasonably supposing an operation in a linear zone, the current of thememory cells of the portion 23 a increases until it reaches thetheoretical value equal to at least eight times the current of thememory cells of the portion 23 apt to the data storage.

It should be noted that by way of a simple system of two equations, withtwo unknown quantities, it can be evinced that the discharge time of theportion 23 a bit line, which is equal to 1/256 or 1/128 of the dischargetime of the bit line, sums the two portions 23 and 23 a.

Therefore, the access time, with respect to the only Bl, of the portion23 a, is drastically reduced, even if not enough to take it again to arandom access time typical of the memories used for running softwarewithout the use of RAM (XIP Flash).

For reaching the object of a reading with access times comparable withthose of a Flash-NOR, in the memory fast portion 23 a, the deviceincludes the implementation of “strapped” approaches both on theword-lines, and on the DSL (Drain Select-Line), and SSL (SourceSelect-Line) as it will be hereafter described with reference to Figuresfrom 14 to 20.

For this reason, the world lines have been managed in a wired modesince, thanks to this measure, the implementation is made possible ofstrap techniques which allow the significant reduction of thepropagations indispensable for the attainment of high performance.However, the wiring of the Wl is not immediately done, more than oneproblem having to be addressed for maintaining both the functionalityand the “integrity of information” for each cell. The proposedapproaches for making the wiring possible will be described in greaterdetail hereafter in a dedicated section.

Obviously, the previous array sizing in the Figure is reported only byway of example of the proposed idea, and it does not exhaust all thepossible combinations within the present invention.

In substance, the proposed architecture allows a user of the solid-statememory device to use it both as a data memory, and as a program and/oroperating system memory. This latter feature cannot be offered bycurrent Flash NAND memories due to the high random access time (>10usec).

As already previously highlighted, so far this lack has been obviated byusing memories of the RAM type wherein the program code or operatingsystem is stored at the start of any electronic device.

Further advantage is given by the fact that the proposed architectureallows a bank of erasable memory to be available with highergranularity, for example 4 kB with respect to 32 kB, since the fastmemory portion 23 a is organized with logic sectors having groups ofonly four plus four cells instead of thirty-two as it occurs for theslow portion 23.

For a better comprehension of the device advantages, we hereafter reporta series of features the new architecture of Flash NAND electronicmemory device 21 allows obtaining. There is a structure with at leasttwo memory areas or portions with high speed difference and the presenceof a sub system with performances comparable with a data memory.Moreover, there are one or more memory portions with very fast randomaccess and comparable with a memory of the NOR type, and the functionalstructure is shared for minimizing the circuit area occupation. The wordline length remains the same (even if with remarkably differentpropagation times) and, in the meantime, the number of bit lines remainsthe same.

The sizes are equivalent to a memory specifically apt to the datastorage function. Features of a conventional data memory in terms ofcompatibility with that of a conventional data memory and arrayefficiency (array/die ratio) of a conventional data memory is retained.A number of masks are employed in the manufacturing process of theintegrated circuit equal to those typically employed for a process ofthe NAND type, with the advantage of employing a more easilyreproducible technology with respect to a Flash NOR and therefore toensure greater yield. There is a lower silicon consumption with respectto the approaches proposed by the known technique in terms of MCP and alower consumption of current. Finally, it is possible to program thememory in the page mode with at least 512 Byte.

This set of advantages is efficiently obtained thanks to the new NANDmemory architecture which will be also defined of the Multi Speed type,as it will be clear from the following description.

According to a further aspect of the present device, which will be nowshown with reference to the FIGS. 1A and from 6 to 13, the architectureof the NAND electronic memory device is described in detail whereininside the cell matrix the word lines are short-circuited in pairs andthey are associated with a single source selector.

Obviously, the previous array sizing of FIG. 6 is reported only by wayof example of the proposed approach and it does not exhaust all thepossible combinations. A selection of the matrix rows is thus providedso as to minimize the decoding network and facilitate the realization ofthe memory device.

As it is well known, in the traditional architectures the word lines ofa matrix are independent from each other and distinct from those of anyother physical sector, i.e. the potential for selecting the cell to beread is applied to one and only one matrix row.

On the contrary, in the memory device 21, each single sector, which willbe hereafter defined “logic sector”, incorporates groups of wired Wlobtained by short-circuiting with each other pairs of “homologous” Wl.Two and four are the most advantageous multiplicity of wiringcontemplable but also, higher multiplicities, of eight and more can beused.

For example, FIG. 6 shows an embodiment of a wiring of two word lines Wlwherein the first row of a physical sector has been short-circuited withthe last row of an adjacent physical sector, obtaining a logic sectorwhich becomes for this architecture the smallest unit being entirelyerasable.

Obviously, nothing forbids that this coupling can occur with differentassociation modes between pairs of word lines. For example, the n-th rowof a physical sector can be short-circuited with the n-th row of theadjacent physical sector, i.e. with the row having the same positionwithin the adjacent physical sector.

It is thus understood how the possible coupling combinations arenumerous. Moreover, these examples are valid in the case wherein amultiple of two has been chosen for the coupling of the word lines of agiven logic sector, thus with word lines coupled in pairs. Theassociation process can be extended to all the physical sectors and withthe desired multiplicity.

It should be noted that in the illustrated architecture only one sectorSSL_ij of source line SL is provided for each pair of adjacent physicalsectors, i.e. one single SSL for each logic sector. More drain selectors(DSL) are provided according to the implemented wiring multiplicity.

With this measure, as it will be hereafter made clearer, the singlelogic sector (which can be functionally defined as such) comprises allthe groups having the wired Wl. In a conventional NAND memory, thephysical sector only includes an SSL, a DSL, and the W1 belonging to thegroup defined by the two selection lines.

Thus, there is a fundamental difference between the definition of logicsector and the physical sector of a conventional matrix. A consequenceof this feature is that the sizes of the logic sectors between the twoportions 23 a and 23 can be different since the elemental structure ofthe same portions is different.

In particular, for low wiring multiplicity, for the fast portion (23 a)there are logic sectors being smaller than the corresponding slowportion (for example, for a multiplicity 2 there is a sector size of 4+4rows, against a size of 16/32 rows of the slow portion). The portion 23a is characterized, generally, by smaller logic sectors. The granularitywith respect to the erasing is thus higher and is a further advantage ofthe device.

The integrity of the selection of a given cell is thus ensured by thedrain selector, which must be maintained distinct for preserving theunivocality of the row decoding operation. In FIG. 6 the presence of theupper drain selector SEL_i and lower SEL_j is to be noted. With thistechnique the matrix rows are biased at least in pairs or in groups offour, eight etc. . . . according to the multiplicity of association andgrouping of the word lines.

FIG. 8 schematically shows a wiring embodiment between four Wl which, ina conventional matrix, would have four physical sectors and which havebeen instead incorporated in a single logic sector having a singlesource select line SSL and four respective drain selectors.

It should be highlighted that the wiring between more Wl allows reducingthe number of drivers necessary to stimulate the selection of thedifferent selection lines. In fact, in a conventional Flash_NAND memory,taking into consideration a generic physical sector, as many selectionnetworks are needed as many the Wl (16, 32, . . . ), SSL (1) and DSL(1)) are with the great difficulty of realizing the networks in an areawhose height is of a single elemental NAND structure. This results in adisadvantageously cumbersome layout due to the very reduced availablespace.

The wiring requiring, besides a modification of the decoding networkwhich will be described hereafter, allows reducing both the complexityof the same and the number of the necessary networks themselves. Theavailable height for its execution is equal to the number of elementalstructures recalled by the multiplicity of wiring (2, 4, 8). A veryadvantageous executive condition derives wherein simplified networks areimplemented in generous spaces making relaxed layouts, distant fromtechnologically difficult passages and, as a matter of fact, engagingdefinitely more reduced areas.

Obviously, the higher the number of wiring of the word lines, the wideris the facilitation of the structures that interface to the matrix. As aconsequence, with this wiring method, there are a high number ofinterconnections and the fragmentation of the same decoding network.

A row decoding is also provided suitable to manage a differentorganization of the wired Wl, so as to make it functional and at thesame time to simplify its network and reduce its global number oftransistors. In fact, the typical one-to-one decoding scheme of theconventional NAND memories cannot be applied to the fast matrix portion23 a as that of FIG. 6 or 8 with word lines of the wired type.

FIG. 14 shows the update of the row decoding relative to the wiring of 2Wl. As it can be observed the decoding scheme involves the lines of twoelemental structure (two being the multiplicity of wiring considered),it lies on a single selection block (Block_i&j) which controls theenabling/disabling of the single management MUX of the sectorpredisposed for the stimulus of the W1 (4 lines), of the DSL (2 lines)and of the SSL (1 line). The inputs of the MUX are connected to the busof the rows (4 lines) whereas the outputs are connected to as many pairsof wired Wl. Moreover, the same MUX controls the communication betweenthe bus of the drain selection lines (DSL_Up & DSL_Dw, which are doubledin case of multiplicity four) and of the source selection line (SSL.)which instead is single no matter what the multiplicity is. More indetail the selection bus of the drain lines associates the DSL_Up withthe selection of the elemental group i (Sel_i) whereas the DSL_DWassociates the selection of the elemental group j (Sel_j). The solutionof the block i&j is ensured by the control of the Block_bus.

The present scheme, compared to an analog decoding of a conventionalNAND, against two elemental structures, employs a single control blockand a single MUX (2 blocks and 2 MUXs for the conventional one) with aconsiderable savings of devices (four transistors for the rows, only onefor the SSL). The combination of this simplification with the doubleheight due to the pair of interested elemental structures makes thegreater realization and area saving of the present memory evident.

Thus, in the end, the wiring of the Wl has inspired an advantageoussimplification and a better implementation of the stimulus structureswhich however do not represent the only appreciable aspects of thememory device. In fact, by enhancing the parallelism of the Wl andreducing the number of the SSL, the bases are configured for aprovidential strap policy which importantly allows reducing the signalpropagations of the Wl and, thus, to complete that improvement of theparameters which control the reading dynamics.

The described wiring suitably increases the space wherein the bypassconnections can be produced with more conductivity but may be morecumbersome than critical layers allowing fast propagations. The possiblestrap approaches will be described in greater detail hereafter.

The features introduced disrupt the traditional operating mode of aconventional Flash NAND memory. In the first part of table 1 (TAB_1) ofFIG. 9 the biasing conditions of a conventional Flash NAND memory in itsfunctional activities are reported in detail. Descriptively, suchfunctions can be summarized as follows.

Reading: in the selected sector all the W1 are maintained at logic level‘I’ (V_read) except for the W1 which identifies the cell to be readwhich is maintained at logic level ‘0’. All the Bl Even or Odd are readthus reading a big page (from 512 bytes to 2 k_bytes). The bank which isnot the object of the reading is forced to Gnd for eliminating effects(disturbances) of adjacency between Bl.

Erasing: in the selected sector all the W1 are forced to Gnd, and the Blare left floating whereas the well substrate is raised up to the erasevoltage (20 v). All the cells belonging to the sector made of a singlestripe of NAND structures are erased.

Programming: in the selected sector all the W1 are biased to 10 vwhereas the WI which identifies the cells to be programmed issubsequently raised up to the program voltage (18 v). The pattern isforced onto the Bl. Those which are forced to Gnd are programmed andthose which remain high are not programmed. The programming involves theentire bank Even or Odd. The B1 of the bank that are not an object ofthe programming are forced to a high level for protecting them from theprogramming.

All the lines of a generic logic sector are managed in an individual andindependent way, thus no particular attention has to be paid.

In the present memory device some functional activities need suitableadaptations so that the operability is ensured even in the presence ofsignificant modifications produced in the array (wiring of Wl, newstructure of the sector). However, for reading and erasing, thefunctions at issue maintain themselves identically. For erasing it isspecified that in the sector involving a numerosity of elementalstructures equal to the multiplicity of the wiring, the wholemultiplicity of structures will be erased. The reduced size of the logicsector according to the memory device, advantageously, allows improvingthe erase granularity.

FIG. 10 helps to explain what happens in the matrix during the readingstep of a cell content. Substantially, the reading step can be performedas in a NAND memory of the traditional type.

In this case an adjusted voltage value V_reg is applied both to thedrain selector of the portion involved in the reading and to the wordlines of the cell to be read. Exclusion from reading the cell which ison the short-circuited word line is ensured by the low potential value(0 V) on the selector SEL_j pertaining to the short-circuited word line.

In a completely analogous way it is possible to graphically follow whatoccurs in the erasing step by making reference to the example of FIG.11. In this case, it is possible to erase the content of cells of anentire logic sector of the matrix by maintaining the potential floatingon the bit lines, applying a biasing voltage value equal to 0 V to allthe word lines of the logic sector, and raising up the potential of theP-Well which physically contains the cells in the semiconductorsubstrate. The rows of the other logic sectors are instead maintainedfloating.

It is important to remember that, in the architecture, a logic sectorcomprises all the cells in wiring and not only those belonging to asingle physical sector of a NAND structure, as occurs instead inconventional contexts. In other words, a logic sector involves NANDphysical sectors in multiples of two, rather than a single packet.

The programming activity is more delicate. The programming activityinduces a significant amount of disturbances and cells which would nothave to be modified are undesirably corrupted. The fields duringprogramming are high and where programming is not desired, theelectrical stresses can be high and cause undesired variations mayoccur.

For that reason, generally, the bank which is not the object of theprogramming is pre-charged at a suitable voltage. Such a measure,facilitating dynamics of ‘auto_boosting’ in the pre-charged structures,allows to containing and limiting the effects of the disturbances. Thefields are reduced by the auto_boosting and thus the efficiency of thedisturbances is downsized.

The programming disturbances would be even more stressing in the memorydue to the plural selection of the word line which intercepts the cellto be programmed and the need to exclude those which, although connectedto the same word line, should not be programmed. For that purpose,following the example of the normal programming, so as to preventdangerous operating contexts, before proceeding to the real programmingstep, a program inhibit condition is set by activating all the DSL linescontaining the word line involved in the programming and forcing acontextual pre-charging of all the NAND structures of the logic sector.In this way a configuration is obtained with inert conditions of thenodes which do not belong to the modification activity, as it will beclear hereafter.

In the second step all the DSL lines not associated with the packetcontaining the cell in the modification step are deselected and thepattern to be programmed is simultaneously configured by forcing apotential of 0 V on the bit lines BL of the cells to be programmed andleaving the pre-charging potential on the cells whose content is not tobe modified. The programming of the entire logic sector provides as manymodification activities as the multiplicity of wiring of the logicsector and coordinate scan of the stimulation of the drain selectionlines (DSL). During the whole programming operation, the line SSL ismaintained at 0 V so as to avoid any path towards ground.

Referring to the example of FIG. 12, let's suppose that the cell to beprogrammed is in place on the second row ROW_2 and on the column or bitline interested in the program pulse Pg. As highlighted in FIG. 12, theprogram pulse provides a potential of 0 on the bit line of the cell tobe programmed, whereas the adjacent bit lines are biased at the supplyvoltage Vcc which excludes the possibility of programming thereof.

According to the structural modification provided by the present memorydevice, two rows of the matrix logic sector are biased with therelatively high (18 V) program voltage. However, the lower rowassociated with the row ROW_2 to be programmed is excluded simply bymaintaining a potential of 0 V on the drain selector SEL_j of relevance.With this the relative intercepted and pre-charged sectors are left inthe inhibit condition. This occurs also for the selectors SEL_h andSEL_k of the logic sector which is not to be programmed.

On the diagram of the timed signals of FIG. 13, it is worth noting thatthe real programming step occurs in two stages or two steps. A firststep provides the programming inhibition with the drain selection signalraising up to the supply value Vcc both for the higher selector and forthe lower one, and with the relative channel pre-charging.

At a second stage, the biasing of the upper selector is maintained atlogic level ‘1’ whereas that of the lower selector is brought to logiclevel ‘0’ protecting the pre-charge of the underlying structure.Simultaneously, the word line is enhanced to 18 V realizing the realprogramming. This fact allows adjusting the program timing so, that inspite of the fact that the word lines are short-circuited, the incidenceof the disturbances are however limited.

The biasing values of the various nodes under the different operatingconditions are shown in FIG. 9 in comparison to the conventionalapproach. In the same table of FIG. 9, the management conditionsrelative to the wiring of the lines SS L only are also shown.

Therefore, the present invention also relates to a programming method ofthe memory device 20 which provides that each programming step of one ormore cells in parallel is preceded by an inhibition step of theprogramming obtained by activating all the drain selection lines DSLcontaining the word line or lines interested in the programming, and,forcing a simultaneous pre-charging of all the channels of the cells ofa given logic sector. A subsequent programming step selects all of thedrain selection lines DSL not associated with the packet containing thecell in the modify step.

Moreover, the pattern to be programmed is configured by simultaneouslyforcing a potential of 0 V on the bit line BL of the cells to beprogrammed and maintaining the pre-charging potential on the channels ofthe cells whose content should not be modified.

Pairs of drain selectors are provided according to the multiplicity foreach logic sector. Differently, only one control terminal is necessaryfor the different source selectors of a generic logic sector since thesame, being wired, are simultaneously stimulated without causingmalfunctions. Among the different stimulated source selectors, only theone aligned with the selected drain will be active.

The source selector of a logic sector is distinct from the correspondingsource selectors of other logic sectors. With equal memory sizes, alogic sector of the matrix corresponds to at least one pair of physicalsectors of a matrix with NAND architecture of the traditional type. Withthe architecture the array is more easily retraceable and equallyfunctional with respect to a traditional NAND architecture.

It is also important to note that for reducing the word line accesstime, which is one of the main parameters concurring to the read andprogram performance of the memory, it has been thought to implement astrap technique. Already used in other types of non-volatile memory, thestrap would be an excellent approach for reducing the propagation timesof the Wl, but, at present, difficult to implement it in a conventionalFlash NAND memory: the space available for technically performing it istoo small.

In fact, a conventional NAND memory has the cells so reduced in sizethat only word lines are admitted having a minimum pitch being so smallas to make the implementation of a technologically complex techniquesuch as the strap physically difficult. For realizing a strap, in fact,it is necessary to have sufficient spaces as to effect contacts andprepare bypass paths with less resistive layers, such as metal. Theselatter are, however, technologically more cumbersome and they need wide‘passageways’ for developing themselves; widely exceeding the pitch ofthe W1 (much more reduced) in their implementation is substantiallydifficult.

Moreover, a conventional Flash NAND, has the peculiarity of having allindependent control lines (W1, DSL and SSL) whose high number wouldimpede the same large number of shunts necessary to perform a strap. Asa matter of fact, the number further exasperates its difficulty. Thecombination of the two features (greater space of each line and highnumber of the same) is a difficult hurdle to overcome toward any strapmode.

However, thanks to the introduction of the innovative method of the rowselection, as previously shown in the descriptive part pertaining to thewired word lines, and thus thanks to the possibility of simultaneouslyselecting two or more rows and the coordinate melting of the SSL in asingle line, the implementation of the strap can be not only realized asshown in FIG. 15 but also leads to obtain word line propagation delayscomparable, if not even lower, than a traditional NOR architecture.Considering a wiring of multiplicity two, it has been said, that twoelemental structures are involved each involving 4 cells NV. In thiscontext, against a number of 12 necessary independent lines with aconventional management, only 7 (4_W1+2_DSL+1_SSL) are needed with thewiring technique (FIG. 6).

Similarly, considering a wiring of multiplicity four, in place of 24conventional lines, only 9 (4_WL+4_DSL+1_SSL) are needed (FIG. 8), aremarkably lower number which frees a more than sufficient space for theexecution of the strap. Therefore it has been possible to devise anadvantageous strap technique by acting on three basic elements;incorporation of more elemental structures in a single sector; wiring ofall the homonymous lines of the elemental structures; and combination ina single selection line for the SSL for each logic sector.

The force of the three concepts allowed by the new functional strategyhas been expressed, thus, resulting in a great reduction of the numberof independent lines necessary for the management of the single logicsectors. Therefore, the number of the shunt lines which make the strapis definitely downsized, permitting the feasibility thereof withoutlosing the minimal size of the cells (an indispensable condition tomaintain the greatest compactness of the memory).

The orchestration of the three explained concepts, which does notmodify, as it has been seen, the functional features of the memory, hasmade the processing of the different strap typologies possible:

1. Border strap (example FIGS. 16, 17A)

2. Full middle strap (example FIGS. 17B, 18B, 20B)

3. Partial middle strap (example FIG. 20A)

4. Distributed middle strap (example FIG. 19)

Hereinafter the different types of straps are specified and shown in theannexed Figures which make reference to the realization of straps insectors mainly having multiplicity of wiring 2 to 4;

The ‘border_strap’ is an edge wiring characterized by strap contactsbetween homonymous lines carried out with ‘scalar’ technique. This is inorder to have the space necessary for their execution. The shortsbetween the homonymous lines are realized in metal_1 whereas the strapsare realized in metal_2.

The ‘full middle strap’ is a “complete wiring” inside an array whichrealizes the strap, ensuring the continuity between homonymous lines ofconsecutive blocks. The shorts between the homonymous lines belonging todifferent elemental structures are realized in metal_1, whereas thestraps are realized in metal_2, and the continuity between the lines ofadjacent blocks is maintained via poly_2.

The ‘partial middle strap’ is a middle strap limited to some lines,carried out in more different combinations; less cumbersome than thecorresponding ‘full,’ it has the purpose of being as ‘transparent” asthe occupied space inside the array.

The ‘distributed middle strap’ is the sum of all the ‘partial middlestraps’ which, in succession and in a distributed way, realize one ormore complete straps with the feature of a propagation as fast andtransparent as occupied space.

For each pair of blocks sharing the same drain contact, commonword-lines with relative shunts in metal 2 in the middle of each submatrix are provided. In substance, for pairs of matrix sectors sharing asame drain contact, common word-lines are provided with relativemetallization shunts in the middle of each sub matrix.

The same source SSL selectors are short-circuited, whereas the effectiveselection of the cell exclusively occurs by way of a drain selector, asshown, for example in FIG. 18 in “full middle strap” mode.

As a general rule, one strap per sub matrix could be enough. However,analyzing the structure of a typical NAND array more in detail, it isobserved that in vertical ground lines in metal1, each having 128 bitlines, and vertical vias of P-well, each 512 bit lines are provided.

Considering the great number of P-well vias existing in a typical NANDarray, and thus the possibility of adding different strap points, thepropagation times are so reduced as to be comparable if not even lowerthan those of a corresponding Flash NOR (i.e. <20 nsec). This approachis contemplated in the examples of FIGS. 19 and 20.

A full strap would imply a greater space than the distributed strap,and, it would be advantageous in the case wherein it is realized at theextremes, i.e. with the contacts at the edges of the device. Adistributed strap can instead be repeated more times at zero cost and italso allows a drastic reduction of the word line propagations.

The strap provided in the present device is compatible with all thememory user mode operations, in particular the read and program stepsare the same with respect to a structure without strap. Regarding theerase operation, the execution granularity of the same doubles withrespect to the elemental structures since it is not possible todistinguish a structure inside a pair. This, however, does not penalizethe memory's general performance since it exclusively relates to thecode portion which has a higher granularity with respect to the dataportion.

It is possible to further relax the pitch of the strap lines in metal_2by repeating the exposed method to two or more pairs of blocks, forexample, as shown in the FIGS. 17A, 17B, 21 for the case of 2 pairs.

If, in this regard, it is to be highlighted that the described straptechnique is easily applicable to the data memorization portion (>=16cells, as shown in FIGS. 22 and 23). FIG. 23, in fact, shows anadvantageous realization of border_strap which can be easily implementedat the matrix edges (but it could be thought also only at the ‘front’);with this the propagation reduces to ¼ of the traditional one. Thecontacting does not suffer from particular difficulties since, with ascalar approach, the swells of the contacts do not meet difficulties tobe carried out and the strap lines are perfectly feasible; only 19 lines(16_row+2_DSL+1_SSL) in place of 36.

The access time of the code portion thus refers to a random access timetypical of the memories used for running a software without the use ofRAM (XIP Flash), i.e. <100 nsec. The approach allows reducing in asignificant way the word line delay partially responsible for thelimited performance of the NAND architectures in reading. Moreover,thanks to this measure, the implementation of strap techniques ispossible. Such techniques allow the significant reduction of thepropagation, which is indispensable for the attainment of the highperformances.

The previous example of array sizing is reported only by way of exampleof the proposed idea and it does not exhausts all the possiblecombinations. Among the other advantages offered by the wired word linesapproach is that of allowing the freeing of wide spaces for theimplementation of the row decoding of a non-volatile memory withsub-micrometric lithography, in particular is especially suitable foruse in NAND architectures, eliminating criticality or extremefragmentations of the row decoding networks.

The principles of the present memory device are easily extendible in thecase wherein it is necessary to provide plural memory portions havingdifferent access speed and data storage capacity, all however being partof a same integrated electronic device.

For example, FIG. 24 schematically shows how a device can be organizedwith a slow matrix portion, a fast portion and an intermediate portionhaving a speed, in turn, intermediate between the two preceding ones. Inthis case, it is enough to provide two functional interruptions of thebit lines with interposition of associated pass transistors.

Advantageously, the portions 23 and 23 a, respectively slow and fast, ofthe non-volatile memory cell matrix 22, communicate with the respectiveinterfaces by way of a communication protocol which manages the entirememory device 20, integrating the “hard disk” and boot/code ROMfunctions.

The device thus exhibits very different functional/performance aspectswith respect to the products of the traditional flash_NAND type. Infact, the memory incorporates slow functional parts, other fast partsboth enhanced by further improvements which involve both flexibilityaspects (addressing multiplicity), and of immediacy (possibility ofrandom access both onto the entire memory and into any data array).

These new potentialities, for a better explanation thereof, havesuggested an enriched stimulus interface (Pin_Out), with respect to atraditional. Flash NAND, with a further address bus and an associatedenable pin PA (paralle_Address). The new addressing structure adjacentto that typical of the traditional Flash_NAND has produced a newcommunication protocol.

Such a protocol has been developed in such a way as to respect thosefeatures which optimize the performances of the device in terms offlexibility and compatibility. In particular, it is compatible with theconventional NAND protocol for the read and modify operations (programand erase), and there is random access of the NOR-like type for anysufficiently wide portion of the memory. Moreover, the speed in therefresh operations of the whole memory, the binary number of the addresspins, the address register charged in a single clock pulse, theinvariance of the address system/bus with respect to the memory sizes,and the synchronous reading in the random modes are particularlyadvantageous. The addressing mode is of the “address bus free” type, andswitchings between the various operating modes are of the “command free”type. Control signals are of the NAND protocol; there is a singlecontrol signal for switching between the various modes, and the singlenon-parallel read mode is by default the NAND one.

For completely exploiting the intrinsic potentialities of thearchitecture, a suitable reading method is to be defined which can be asflexible as to pass from an operation mode to the other withoutresorting to burdensome and slow commands. In this way the memory device20 acts, for a processor with which it normally interacts, really as asingle complex and integrated system of data, codes, information andbase commands for the operating system storage.

The various memory portions 23, 24 and 23 a, 24 a have been designed andorganized so as to be read indifferently with all the modes, except forthe different operation speed which depends instead on the matrixportion which is to be addressed.

The above mentioned features will be clearer from the followingdescription. By comparing the approach of the memory device with theknown approaches, for example with the NAND memory of FIG. 1, it can beappreciated how such known memory device comprises a certain number(sixteen) of address pins and outputs (sixteen).

Both NAND architectures, for example: CL, AL, PR etc . . . , and NOR (W)architectures are also provided with traditional common control pins.The addressing window equal to sixteen has been traditionally adoptedfor obtaining an efficient partitioning of the memory in terms ofblocks, sectors and sub-sectors, and in such a way that the signals canmove inside the memory with simple and “identifiable” loadings of theaddress registers respectively corresponding to the block, to the sectorand to the selected sub-sector. The memory device 20 is capable ofperformances in reading of about ˜100 nsec., which is typical of a NORmemory. Moreover, such device 20 keeps the writing/erasing and, ingeneral, modification performances of a typical NAND memory for datastorage.

To meet these multiple needs, a specific control pin has been provided,shown in FIG. 25 and indicated with the acronym PA, which allows passingfrom a mode of the data storage type to a mode of the XIP type with asimple switch “0->1”, or “1->0” in the opposed case. All this is withoutthe need of using added clock and wait cycles of the microprocessorwhich interacts with the memory.

It is worth noting that the data storage mode makes use only of thetraditional NAND protocol of the synchronous type and it is essentiallyaddressed to the use of the memory as data/files storage. In this casethe control pin PA is kept at the logic level “0”.

The device 20 can also however operate in the parallel access mode.These modes are all referred to the device operation with the pin PAkept at the logic level “1”. Three main modes can be identified, whosewaveforms associated with the signals applied to the device pins arereported in FIG. 26. As it can be easily noted, the first two modes donot require any multiplexing of the addresses in the output pins, asinstead occurs in the traditional NAND architectures.

The first one of these two protocols is of the asynchronous type and itessentially corresponds to a classical asynchronous protocol whichallows addressing up to 1 Mbit of memory at a speed depending on thefeatures of the selected array portion, for example 100 nsec for thepart of the NOR-like type and 20 usec for the NAND part.

The second protocol is of the extended type, and, with the addition of asingle clock pulse it allows addressing up to 64 Gbit by way of theloading of an address register with 32 bit in two successive instants(16+16), thus the reading of a generic data at a speed depending on thearray region wherein one is, for example 100 nsec+clock for the NOR-likepart, equivalent to ˜120 nsec. In both the first two protocols theoutputs are free to switch in the state corresponding to the desiredoperation and/or cell.

A third protocol, called “maxi”, makes use, by way of a multiplexingoperation, of the output pins also used for the NAND protocol to addressup to a maximum of 16 Tbit. In two successive instants the address m(middle) part, and the address M part (most, with 8 bits) arerespectively loaded by way of the address buffer and by way of the firstoutput pins <0:7>. Afterwards, with a clock pulse on the pin AL theregister 1 (least, with 16 bits), is loaded by way of the address pinsand the reading is made to start with a speed equal to that of thesecond protocol. The third protocol is functionally distinguished fromthe first two exactly by the use of the pin AL, which is intended forthe definition of the latching operation of the addresses by way of theoutput pins.

Hereafter the main features of the reading step are summarized. Portion23 a, NOR-like tacc, has a max of 100 nsec random access, without limitsand a 30 nsec burst & random access (in page). Additionally, portion 23NAND tacc had a max of 20 usec random access, without limits, and a 30nsec burst & random (in page).

All the memory modification operations make use of the traditionalprotocol used in the NAND architectures and therefore are not detailedin the description. Let's now consider an example of the operation ofthe device. Suppose that at the switching on step of a mobile electronicdevice (cellular, palmtop, camera, etc. . . . ) which incorporates thememory device according to the invention, the content of a part IPL(Initial Program Loader) and of a second part SPL (Secondary ProgramLoader), of the mobile BIOS, should be loaded in a first 1 Mbit portionof the non-volatile memory matrix object of the present invention.

Such a first 1 Mbit portion of program instructions has the peculiarityof allowing a quick access to the cells. At the start-up of the mobiledevice, a reading of the memory is thus performed in the first 1 Mbitlocations (FIG. 5), since the address registers (32 or 40 according tothe architecture) are with regard to the least part, connected directlyto the 16 external address pins, and as for the middle (and most) parts,connected to zero and reset by the power on reset signal. The reading ofthese cells occurs at a speed of 100 nsec. The response speed of thedevice is thus similar to that required by these boot operations andthus it does not need RAM loading.

In contrast to the most developed existing wireless memory devices, allthe read operations performed with the protocol used in the memory donot require additional commands such as, the “load” of a RAM of normallysmaller sizes than the smallest random addressable portion of the memorydevice (32 Kbit with respect to 1 Mbit).

A further important advantage of the described protocol is itsflexibility, since it allows the memory reading both with a conventionalapproach of the NAND type and with an efficient random approach so as tospeed up the responses of the fastest portions (portion 23 a NOR-like,page buffer).

Moreover the passage from a mode to the other occurs without complicatedwait cycles, but rather as function of a single control pin (PA) and itis thus immediate.

In conclusion, the memory device allows the realizing on a single chip,thus using a single technology, a group of functions which up to nowcould be obtained only by associating memory chips realized andstructured with different technologies.

Everything is obtained with an advantageous modification of the NANDmemory matrix, and, it allows the use of a flash NAND structure,substantially substituting a RAM or a ROM, for the start-up step.

From another point of view, the memory and associated method allowsmaking an intimately slow NAND structure with random access. Globallythe device and the method attain a rich series of advantages listedhereafter: reduced costs and low circuit complexity; memory areas(higher or equal to two) at different operating speeds, which can beselected by way of row decoding; memory areas with at least a fullrandom access part, substantially with NOR modes; a memory portion whichcan be used as data storage of greater capacity with respect to theportion apt to the code storage; NAND protocol for the sectors used forthe data and full random access for the part apt to the code XIP; itmakes a RAM unnecessary to execute the code; low assembling costs withrespect to known approaches of Toshiba/Samsung; low costs for the userin the case of use of extra chip RAM; full technological compatibilitywith other associated NAND circuits, for example for the realization ofmemory parts with NOR random access; reduction of the capacitive loadingof the bit lines by way of decouplers; and continuity and sharing of thestructures of the NAND areas at different speed.

Additional features of the invention may be found in co-pendingapplications entitled NON-VOLATILE ELECTRONIC MEMORY DEVICE WITH NANDSTRUCTURE BEING MONOLITHICALLY INTEGRATED ON SEMICONDUCTOR, applicationSer. No. 11/279,381, U.S. Pat. No. 7,397,700; AN INTEGRATED ELECTRONICNON-VOLATILE MEMORY DEVICE HAVING NAND STRUCTURE, application Ser. No.11/279,384, U.S. Pat. No. 7,295,472; and NON-VOLATILE ELECTRONIC DEVICEWITH NAND STRUCTURE BEING MONOLITHICALLY INTEGRATED ON SEMICONDUCTOR,application Ser. No. 11/279,378, U.S. Pat. No. 7,274,594, the entiredisclosures of which are hereby incorporated herein by reference.

That which is claimed is:
 1. An apparatus, comprising: first and secondgroups of series coupled memory cells included in respective first andsecond physical memory portions of a logic sector, wherein a number ofmemory cells in the first and second groups of series coupled memorycells in the logic sector is different from a number of memory cellsincluded in another logic sector, wherein the logic sector and the otherlogic sector have different column capacitances, wherein transistorscoupled to corresponding memory cells of the first and second groups ofseries coupled memory cells are activated by corresponding wordlines offirst and second groups of wordlines, respectively, and wherein arespective row driver is coupled to each wordline of the first group ofwordlines and to each corresponding wordline of the second group ofwordlines to form the logic sector.
 2. The apparatus of claim 1, whereinan access speed of the logic sector is different from an access speed ofthe other logic sector.
 3. The apparatus of claim 1, further comprisingfirst and second arrays of memory cells, wherein the first array ofmemory cells includes the first and second groups of series coupledmemory cells included in first and second physical memory portions ofthe logic sector.
 4. The apparatus of claim 3, wherein the second arrayof memory cells includes third and fourth groups of series coupledmemory cells in third and fourth physical memory portions, respectively.5. The apparatus of claim 4, further comprising a first row decoderbetween the first and second arrays of memory cells.
 6. The apparatus ofclaim 5, further comprising: third and fourth arrays of memory cells;and a second row decoder between the third and fourth arrays of memorycells.
 7. The apparatus of claim 6, wherein the first and second arrayshave a smaller minimum addressable sector size than the third and fourtharrays.
 8. The apparatus of claim 1, further comprising a common sourceselect line configured to select the logic sector.
 9. The apparatus ofclaim 1, further comprising first and second drain selectors configuredto select the first and second groups of series coupled memory cellsincluded in the first and second respective physical memory portions,respectively.
 10. The apparatus of claim 1, wherein each of the firstand second physical memory portions of the logic sector is individuallyaddressable.
 11. An apparatus, comprising: first and second groups ofseries coupled memory cells included in respective first and secondphysical memory portions of a logic sector of a plurality of logicsectors, wherein transistors coupled to corresponding memory cells ofthe first and second groups of series coupled memory cells are activatedby corresponding wordlines of first and second groups of wordlines,respectively; first and second drain selectors configured to select,respectively, the first and second groups of series coupled memory cellsincluded in the first and second respective physical memory portions;and a common source select line configured to select the logic sector.12. The apparatus of claim 11, wherein a number of memory cells in thefirst and second groups of series coupled memory cells in the logicsector is different from a number of memory cells included in anotherlogic sector.
 13. The apparatus of claim 12, wherein an access speed ofthe logic sector is different from an access speed of the other logicsector.
 14. The apparatus of claim 11, wherein a wordline of the firstgroup of wordlines is coupled to a respective wordline of the secondgroup of wordlines.
 15. The apparatus of claim 11, wherein each of thefirst and second physical memory portions of the logic sector isindividually addressable.
 16. The apparatus of claim 11, wherein thefirst and second physical memory portions of the logic sector areaddressable by the first and second drain selectors, respectively. 17.An apparatus, comprising: transistors coupled to corresponding memorycells of first and second groups of series coupled memory cells, whereinthe transistors are activated via corresponding wordlines of first andsecond groups of wordlines, respectively, wherein the first and secondgroups of series coupled memory cells are included a logic sector of aplurality of logic sectors; first and second drain lines configured tobe activated to select, respectively, the first and second groups ofseries coupled memory cells; and a common source select line configuredto be activated to select the logic sector.
 18. The apparatus of claim17, wherein an access speed of the logic sector is different from anaccess speed of another logic sector of the plurality of logic sectors.19. The apparatus of claim 17, wherein the first and second groups ofseries coupled memory cells are included in first and second respectivephysical memory portions of the logic sector, and wherein a number ofmemory cells in the first and second groups of series coupled memorycells in the logic sector is different from a number of memory cellsincluded in another logic sector.
 20. The apparatus of claim 19, whereinthe first and second physical memory portions of the logic sector areindividually addressable based on a selection of the common sourceselect line.